(Solved): solid mechanics The dimensions of the double-box beam cross section shown are b=150mm,d=50mm, ...

The dimensions of the double-box beam cross section shown are $\mathrm{b}=150\mathrm{mm},\mathrm{d}=50\mathrm{mm}$, and $t=4\mathrm{mm}$. If the maximum allowable bending stress is $\mathrm{sb}=17\mathrm{MPa}$, determine the maximum internal bending moment Mz magnitude that can be applied to the beam. Hint: think of the shape as one large rectangle with two "negative" rectangles cut out of it.